cstevenpeterson

My Feedback: (21)

Hi Folks,

I have posted this out of curiosity.

I routinely need to replace the brass fuel lines in my glow tanks with a frequency of about once every year. I run 10-15% glow and I drain my tanks when not flying. I have found again recently that my poor engine performance was due to the brass lines deteriorating to the point where they are corroded through and there are many small particles of brass floating in the tank (I did not have a filter installed). The corrosion usually begins at the bends.

I used to run full size race cars (in my youth) and I know how corrosive methanol can be, but I am wondering if this is typical for a glow fuel tank setup or if I am experiencing an unusual problem with respect to the frequency of the need to replace tubes. Any comments?

Steve

Sport_Pilot

This is an eletrolitic reaction between the brass, metal clunk, fuel, and any water in the fuel. Make sure there is no exposed brass, that is the fuel line is pushed up all the way to the stopper. Consider using a brass clunk, or use alluminum tubing. If you pump your tank dry you won't need to worry about the vent line. Keeping the fuel dry will also help.

cstevenpeterson

My Feedback: (21)

Sport Pilot,

I never really thought about the fact that there are dissimilar metals within the tank and there could be galvanic corrosion taking place - is that what you are hinting at? The tubes are brass and the clunk looks to be nickel plated "something". I also do not have the brass tubes fully covered by the silicon tubing thereby exposing the brass to the "solution". In addition, it makes sense that the corrosion starts at the bend as that has been cold worked (by bending) and I definitely do not have the bend covered with silicon. I need to look at the electro-negativity of aluminum as compared to the other metals present - I guess you are saying that aluminum is a better choice for reducing this problem somewhat?

Thanks for the response - it gives me some things to think about.

Steve

MinnFlyer

My Feedback: (4)

For the dissimilar metals thing to take affect, the two metals must be in contact with an electrolyte (like fuel) AND each other. This is not the case with the clunk.

I think it has something to do with the air in New Jersey.

But seriously, regardless of what's causing it, as long as you have to replace it, next time get some 1/8" COPPER tubing from your local Auto Parts Store. It's very cheap (50 - 75 cents per foot) and it bends very easily without kinking.

Another nice thing about the copper is that since you can get it in long lengths, I like to run it all the way through the firewall. this does away with having a Fuel Line to Metal tubing connection inside the Fuse which could split and leak (Don't ask how I found THAT out).

Here's a pic I took to show just how easily copper bends

cstevenpeterson

My Feedback: (21)

MinnFlyer,

Thanks for that info. You're right about the metals being in contact - I guess I am not thinking too clearly about this (could it be the air?). I am going to the auto parts store at lunch to check out the copper tubing. I can probably get it at McMaster Carr also. As for the air here, I live near and my wife is from PA, when she moved to NJ, I told her we had to change the air in her car tires so they would pass inspection in NJ!

Steve

paladin

My Feedback: (9)

Brass 101

Brass is a mixture of copper and nickel. The % of each used is what governs the hardness. The more Cu the softer and easier to machine (in our case bend). Brass is not heat treatable nor is it cold workable (cold working implies that if flexed beyond the plastic limit without braking the material gets stronger) it comes in soft, half hard (what we use), and hard. Brass is very susceptible to fatigue which makes it poor in applications where it is exposed to vibration.

Two of the clubs I belong to have noise regulations and they are usually set lower than most manufacturers mufflers will provide so one way around this is to add a stinger to the muffler out let or add internal baffling. The most available material in the sizes we need is brass. All of the brass inserts/stingers will eventually crack due to the engine vibration. Now in the fuel tank we have the ability to isolate the brass from vibration and it will perform its function for a long time. If some how it gets a vibration it will fail. My personal favorites are the ARF’s that capture the plug of the tank in the firewall. These usually come with aluminum tubing because brass would not last failing due to the transmitted vibration.

I’ve experience a number poor or short engine runs caused by broken brass. I’ve even had brass clunks break. Fix the fuel cell and reinstall it making sure there is no place it is rubbing against the fuse and the problem should be gone for a long time.

Good luck

Joe Felice

MinnFlyer

My Feedback: (4)

Ah yesssss... Getting the car ready for inspection. What memories THAT brings back. I grew up in the Northeast corner of The Garden State. Still have a sister living there. It really is beautiful, especially your area.

PS, No Car inspections here in MN

JimTrainor

A while back this subject came up and tweaked my curiosity so I stick a brass tube and a nail in some fuel and measured the resulting voltage and current. It was 150 mV and 0.3 uA. I don't know what it woudl be with aluminum... but it woudl be something, and the brass is the material that is corroding as electrons are stripped away. Using aluminum tubing would help matters as well.

http://www.rcuniverse.com/forum/m_37.../tm.htm#379179

Ross Kean

I think you will find that brass is a combination of copper and zinc (not nickel). Composition can vary quite a bit with different alloying elements depending upon the application.

Ross

paladin

My Feedback: (9)

Ross is right it is zinc.



They don't have inspections in MN? Whats up with that? How do the garages stay in buisness?

Jim Thomerson

The solution is to use copper tubing, not brass.

Jim

cstevenpeterson

My Feedback: (21)

Hi Folks,

I decided to try using both copper and aluminum in different tanks as a test. I picked up some copper tubing at the auto parts store for $.75/ft and I also picked up a few pieces of aluminum tubing from the LHS. I will re-plum this tank with one of the materials and then another tank with the other material and we'll see what the results are. I guess we could analyze this to death but I just feel like trying something. It may be a while, but I will resurrect this post when I get some results. Thanks for the feedback.

Steve

MinnFlyer

My Feedback: (4)

Cool, I'll be very interested to hear the results

Sport_Pilot

Well I have had no problems with the aluminum tubing, and little with brass. But as others have suggested, copper should be better yet. Copper tarnishes and builds up a protective platenia.

Sport_Pilot

Actually the metals being in contact hastens the effect, there is still a reaction if both are submerged in a electrolyte. You can make a galvanic cell by submerging strips of two dissimilar metals in an electrolyte, if you put a voltmeter at each of the strips of metal you will measure a voltage at each one. The less noble of the two metals will corrode. With a strong electrolyte such as salt water and a very noble metal like say gold and a very unnoble metal like lead or zinc you will have a strong current and large voltage difference, and you can notice the corrosion in just minutes. If you replace the electrolyte with a week one, such as freshly boiled distilled water you may have the same voltage but the current will be very low and it would take days or weeks to notice the corrosion. If you disconnect the voltmeter from the strong cell you will still have corrosion on the less noble material but it would also take a considerable amount of time. In the latter case the current if flowing in both directions in the electrolyte. The latter effect is what happens when steel rusts in air without touching another metal.

So the solution is to use more noble metals such as copper, use a weaker electrolyte such as fuel with less water or less nitro, or to use a sacrificial anode such as adding a hunk of zinc or lead into the tank. Since the latter would dissolve into the fuel I don't think the sacrificial anode is such a good idea.

Bent brass is worse because it separates the crystals of zinc and copper, the zinc then easily corrodes because it is no longer protected by the copper. This leaves a very brittle material of porous copper.

Pure aluminum is less noble than copper but more noble than zinc. Aluminum alloy is much better but would suffer the same problem as brass if bent.

I think that one magazine expert said that the brass creates a catalytic effect with the fuel and creates an acid. I don't know if this is true but nitro is already a weak acid. It is not strong enough to eat through the metal from its acidity as I think the PH is only about 6.7 or so, but it should be a fair electrolyte.

Dsegal

It was Joe Wagner who wrote in the November 2002 issue of Model Aviation:

"...the brass tubing and clunk weights can catalzye the methanol in glow fuel into acetic acid. That's a guaranteed rust inducer. Since then I have stopped using brass for fuel tubes. Copper and aluminum are okay, and so is plastic."

jessiej

Copper from the auto parts store is inexpensive, lasts seemingly forever and is easily worked and soldered.

jess

paladin

My Feedback: (9)

Looking at this from an engineering standpoint I know that the galvanic action only it present in the presents of a catalyst. So the first thing I would do id consider the amount of time the tank is filled with fuel. I’m in the north so, while I winter fly the majority of my flying is in the warm months so I figure I have fuel in the tank 4 hr a week that is 208hr a year. For me the galvanic action would take 10+ years to do its work which my maintenance records support (actually 15 year average). Now if the average failure of brass is after 208 X 15 = 3120hr and the risk is relatively low, (No other system is damaged by the failure) that makes it a good candidate for this application. But first we need to look at the fitness of the other materials and conditions. Over that 15 year period that brass spends the majority of its time in a atmosphere of high humidity with corrosive vapors from the left over nitro, & alcohol (164hr/wk X 52wks X 15yr = 127920hr of exposure). Given the amount of time it is left “idle” it has to be considered.

Aluminum while it seams to hold up better in the galvanic(from previous text and experience) and in the idle area has a problem with leakage. Aluminum oxidizes very quickly and that prevents a good seal between the stopper and the tubing. While a minor problem it means having to watch it for signs of this failure. It also leads to the failure of other systems usually after a few years the plastic stopper plate in the tank strips due to over tightening. I would definitely not use this setup on a pressurized system.

Copper I would think the galvanic action would be worse with Cu but I am an ME and would need and EE’s input. As an ME my main concern would be the idle time and copper oxidation Copper sulfate being one of those possibilities (but a CE would be the one to make the call on that). What I know about is Copper sulfate has the ability to dissolve (suspend) in liquids thus can be transported to the engine and when combustion occurs it is very likely that some of it will come out of suspension and deposit in the engine. Copper sulfate is very corrosive! It is what gives the statue of liberty its color and have you noticed that if you pick up a tank from your used once a long time ago box it usually had a green hue to it, I think that is copper sulfate. Risk of multi system failure I think is very high with the use of copper as it does not have the protection from corrosion that brass has.

Joe Felice

Steve Collins

My Feedback: (8)

????????? I don't know what this is all about since I have never, ever, had this happen in 25 years of using glow fuel. I currently have a number of planes that have been in use for 5+ years and there are zero problems with the brass tubing.

If you insist on a solution, the best fix is to use a tank that doesn't use metal tubing. Hayes tanks are the best. Great Planes tanks will do.

Sport_Pilot

No two completly differant things. Galvanic action is the flow of electrons from one metal to another. Catalytic reaction is when any materail influences the reaction of another without being part of that reaction. For example our glow plugs attract nitrogen and carbon, thus leaving the hydrogen atoms better exposed to the air. Galvanic reaction does not do this.

Rodney

The big culprit here is the nitro. Nitro will definately eat holes in the brass, the higher the nitro content of your fuel, the more rapid and severe the problem.

NJ Georgee

My Feedback: (3)

Thats why i started using after run oil, After I got a mouth full of nitro when sucking fuel to my carb WoooooWeeeee that stuff is worse than gas in the mouth...lol

Sport_Pilot

Nitro will definately eat holes in the brass

This is way off base. Nitro is a very very mild acid. I have left fuel in old brass C/L tanks for years with no corrosion. It is however a conductor of electricity, thus a good electrolyte.